St. John Damascene (d. 749AD) is perhaps known for having written a summary of Christian theology and beliefs (An Exact Exposition of the Orthodox Faith), which was in fact his own synthesis of the Patristic writers who came before him.
St. John describes how Satan and demons came into existence and his description of the existence of evil reflects the commonly held views of his day. Satan is NOT God’s opposite and equal – far from it. Satan and demons have no power except what god allows them to have (One can think of the Gospel lesson of the Gadarene swine where the demons have to ask permission of Christ to leave the man they had possessed. The demons do not even have power over swine, as is stated and prayed in the pre-baptismal exorcism prayers).
This has to do with God’s own respect for the free will He has bestowed on some of his creatures including both humans and angels. Neither humans nor angels are automatons – preprogrammed beings that have no choice in what they do. We can freely choose good or evil, just like the angels. However in terms of having power over our lives, Satan and demons are limited by what God allows them to do, AND by our own cooperation with them. For neither Satan nor angels can make us do anything either. They cannot violate our free will. The will of God and the will of any human are thus both limitations put on the power of the Evil One.
St. John Damascene writes:
“Among the angelic powers the chief of the terrestrial order, the one to whom God had entrusted the task of looking after the earth, was not evil by nature, he had not received any trace of evil from his Creator. He was good. However, he did not maintain the light and honor that God had given him. By a deliberate act of his own free will he rebelled against the Creator. He turned his face away from goodness and fell into evil. Evil in fact is merely the absence of good, as darkness is the absence of light. A host of angels placed under his command followed him in the fall. Despite their angelic nature, they also freely plunged from goodness down to evil and became wicked. The devils cannot do anything against us without God’s permission. But with God’s permission they are powerful. All wickedness, all the passions are inspired by them. But listen: God allows them to suggest sin to a person, but they cannot force him to do it. We ourselves are responsible for accepting or rejecting their seductive suggestions.” (Drinking from the Hidden Fountain, pp. 127-128)
In every Orthodox Baptism, we pray over the baptismal candidate:
O Lord of Sabaoth, the God of Israel, Who heals every malady and every infirmity: Look upon Your servant; prove him (her) and search him (her) and root out of him (her) every operation of the devil. Rebuke the unclean spirits and expel them, and purify the works of Your hands; and exerting Your great power, speedily crush down Satan under his (her) feet; and give him (her) victory over the same, and over his unclean spirits. (3rd Exorcism Prayer)
May we all be so victorious over the Evil One.